1. Field of the Invention
The present invention relates to a curable resin composition as well as a hole-plugging core substrate and a hole-plugging printed wiring board. In particular, the present invention relates to a hole-plugging curable resin composition of a halogen-atom-non-containing resin substrate (halogen-free resin substrate), a halogen-free resin substrate filled with the cured product of the composition, and a halogen-free build-up printed wiring board manufactured by the halogen-free resin substrate.
2. Description of the Related Art
A halogen-containing resin substrate such as a brominated epoxy resin substrate and the like may be used to a core substrate in a printed wiring board and the like from the view point of flame resistance.
However, in view of a recent environmental problems (particularly, a problem of dioxine generated in incineration), a halogen-free resin substrate such as an EP (epoxy) resin substrate and the like is more preferable than a halogen-containing resin substrate.
Incidentally, a conventional hole-plugging resin ink is solely designed and composed to reduce a linear expansion coefficient of its cured product to prevent occurrence of a crack of a printed wiring board (Japanese Patent No. 3739600 and the like).
However, when the inventors manufactured a build-up printed wiring board having a via-on-via structure (that is, a structure in which a via is overlapped just on a via) by filling the through holes of a halogen-free resin substrate with the conventional resin ink and curing it, it was found that a crack-resistant property and various reliabilities (insulation reliability, connect reliability and the like) were greatly deteriorated when three or more build-up layers were formed (that is, when made to a stacked via structure). Specifically, when the build-up printed wiring board was subjected to a cold/heat cycle test, it was found that a crack of an interlayer insulation material (FIGS. 2, (14)), a cutting of a copper foil (circuit copper foil, through hole plating copper foil, and the like, FIGS. 2, (15)), and the like occurred particularly in the vicinity of an outer layer, in the vicinity of stacked via, and further in the vicinity of through holes, and the like at a relatively small number of times of cold/heat cycles.
In view of the above circumstances, an object of the present invention is to provide a hole-plugging curable resin composition preferably used for a halogen-free resin substrate and the like having a small load on an environment, a core substrate, and a hole-plugging build-up printed wiring board having a via-on-via structure (in particular, a stacked via structure) having an excellent crack-resistant property, an excellent insulation/connection reliability, and the like.